Today’s launch in Chicago; Reno, Nev.; Fresno and Sacramento, Calif.; and the region surrounding Los Angeles (though not in LA itself) – coupled with activations on Monday in Atlanta, Seattle and Minneapolis – bring its total upgraded footprint to 23 markets covering more than 100 million people. While T-Mobile doesn’t sell the device yet, customers with unlocked iPhones can use them on the carrier’s network. But only in areas where the upgrade is complete will they get anything beyond a 2G connection.

Though in the rest of country the network officially hasn’t seen the upgrade – which will move a portion of T-Mo’s HSPA+ network to the 1900 MHz PCS band – customers with unlocked iPhones have reported seeing HSPA+ signals from New York to LA, cities where their Apple devices would normally be restricted to pokey 2G speeds. Right up to its launch this week, Chicago was a hotbed of signal sightings so T-Mobile obviously has many more markets in the works.